Gunmen stormed an office of Save the Children in eastern Afghanistan on Wednesday, officials and witnesses said, in an ongoing attack that has wounded at least 11 people.

"At around 9:10 am a suicide attacker detonated a car bomb at the entrance of Save the Children's compound in police district three of Jalalabad city," Nangarhar governor spokesmanAttaullah Khogyani told AFP.

"A group of armed men then entered the compound. So far 11 wounded people have been brought to hospitals."

Mohammad Amin, who was inside the compound when the attackers stormed in, told AFP from his hospital bed that he heard "a big blast".

"We ran for cover and I saw a gunman hitting the main gate with an RPG (rocket propelled grenade) to enter the compound. I jumped out of the window," Amin said.

Afghan TV news channels showed a thick plume of black smoke rising above the compound and what appears to be at least one vehicle on fire outside the office.

Another witness told AFP: "It might be a complex attack. I am hearing gun fire from inside Save the Children compound."

There was no immediate claim of responsibility for the attack. No one from Save the Children's office in Kabul was available to comment.

Nangarhar, a restive province bordering Pakistan, is a stronghold for the Islamic State group and also has a significant Taliban presence.

US and Afghan forces have been carrying out ground and air operations against IS fighters in Nangarhar.

While Afghan security forces are conducting most of the fighting against IS and Taliban militants, US troops operate alongside them in a training capacity and are frequently on the front lines.

Wednesday's assault comes days after Taliban gunmen raided a luxury hotel in the Afghan capital, killing at least 22 people, mostly foreigners.

The attack is also the latest violence to strike a foreign aid group in war-torn Afghanistan.

The International Committee of the Red Cross announced in October it would "drastically" reduce its presence in the country after seven employees were killed in attacks last year.

The decision by the charity, which has been working in Afghanistan for over three decades, underlined the growing dangers for aid workers, who have increasingly become casualties of a surge in militant violence in recent years.